1. Field of the Invention
The present invention relates to a vibration wave motor control apparatus, a vibration wave motor control method, a program, and a storage medium, and more particularly, to a vibration wave motor control apparatus and method for controlling a vibration wave motor adapted to be driven by a voltage of a set frequency, a computer-readable program for causing a computer to execute the vibration wave motor control method, and a computer-readable storage medium storing the program.
2. Description of the Related Art
A vibration wave motor is known, which is adapted to generate a vibration wave in an elastic body comprised of a piezoelectric element that vibrates when applied with a voltage, to thereby relatively move the elastic body and a movable unit disposed in contact therewith using a friction force produced therebetween.
Such a piezoelectric element has a resonance point (resonance frequency) that varies depending on environmental conditions such as temperature, humidity, load, etc. To stably operate the piezoelectric element, the frequency of the voltage applied to drive the piezoelectric element (hereinafter referred to as the “drive frequency”) must be controlled to be always greater than the resonance frequency of the piezoelectric element.
For the drive frequency control, it has been proposed to use a monitor piezoelectric element, i.e., a further piezoelectric element adapted to monitor a vibration state of an elastic body of an ultrasonic motor, which is an example of a vibration wave motor (see, FIG. 1 of Japanese Laid-open Patent Publication No. 05-252765, for instance).
In that case, extra cost is added to provide the monitor piezoelectric element, which is solely used for the drive frequency control. In addition, a monitor signal processing circuit must be provided to process an output signal from the monitor piezoelectric element, resulting in increase in size and cost of a circuit board including a control circuit for the vibration wave motor.